Absorbent foam material, a method of producing it and an absorbent structure containing said foam material

ABSTRACT

A liquid absorbent open-cell polymeric foam material having properties which makes it suitable for use as an absorbent structure in absorbent articles such as diapers, pant diapers, sanitary napkins, incontinence guards, wound dressings, bed protections etc., at which the foam material has an absorption rate at wetting of at least 0.4 ml/s for a round sample having the diameter 50 mm, a liquid distribution capacity at an inclination of 30° of at least 15 g/g and a liquid storage capacity of at least 9% measured through CRC (centrifuge retention capacity), at which the test liquid in all cases is synthetic urine. There is further referred to an absorbent structure containing the foam material.

PRIORITY

The present application is a continuation of U.S. Ser. No. 09/651,130,filed Aug. 30, 2000, which claims the priority of Swedish PatentApplication No. SE 9903071-0, filed in Sweden on Aug. 30, 1999 andclaims the benefit of U.S. Provisional Patent Application No.60/198,451, filed in the United States on Apr. 19, 2000, incorporatedherein by reference.

TECHNICAL FIELD

The present invention refers to a liquid absorbent open-cell polymericfoam material having properties which makes it suitable for use as anabsorbent structure in absorbent articles such as diapers, pant diapers,sanitary napkins, incontinence guards, wound dressings, bed protectionsetc. The invention also refers to an absorbent structure in an absorbentarticle of the above mentioned kind containing said foam material.

BACKGROUND OF THE INVENTION

Absorbent articles of the above mentioned kind are intended to be usedfor absorption of body liquids such as urine and blood. They usuallycomprise a liquid pervious topsheet, which during use is intended to befacing the wearer's body, e.g. a nonwoven material of spunbond type, ameltblown material, a carded bonded wadding etc. They further have aliquid impervious backsheet, e.g. a plastic film, a plastic coatednonwoven or a hydrophobic nonwoven, and an absorbent structure arrangedbetween the liquid pervious topsheet material and the liquid imperviousbacksheet. This absorbent structure may be constructed by several layerssuch as a liquid acquisition layer, storage layer and distribution layerin order to fulfill the functions which are desired in an absorbentstructure: capacity to quickly receive liquid, distribute it in thestructure and store it.

As a liquid acquisition layer there is usually used a porous materialhaving a high momentaneous liquid receiving capacity. Such materials areopen, bulky structures with large capillaries, for example cellulosicfluff pulp of thermomechanic or chemothemmoechanic (CTMP) type,chemically stiffened cellulosic fibers, synthetic fiber structures ofdifferent types and porous foam materials etc.

As a storage layer there is usually used cellulose fluff pulp mixed withso called superabsorbents, which are polymers with the ability to absorbseveral times their own weight (10 times or more) of body fluids. It isalso possible to use an absorbent foam material as a storage layer. As adistribution layer there can be used cellulosic fluff pulp, tissuelayers, foam, synthetic fibers and the like having high liquiddistribution capacity. It is also possible to combine two or more of thefunctions acquisition, storage and distribution in one and the samelayer.

It is previously known through U.S. Pat. No. 3,512,450, EP-A-0 293 208and EP-A-0 804 913 to use a compressed foam material of regeneratedcellulose, e g viscose, as an absorbent structure in an absorbentarticle of the above mentioned kind, e g a sanitary napkin. The articlemay then be made very thin and still have a high absorption capacity.The compressed viscose foam expands quickly in the z-direction whenliquid is absorbed by the material when wetted.

The production of absorbent foams based on polysaccharides by foaming anaqueous solution of a polysaccharide and a surfactant by mechanicalagitation or gas supply, and Then stabilize the foam by crosslinkingwith a covalent or ionic crosslinking agent, is previously known throughWO 94/00512 and EP-A-0 747 420. The foam may for example be used as acarrier material in medical applications and in wound dressings. Nothingis mentioned about specific absorbent properties.

WO 95/31500 describes the production of absorbent porous foams having amean pore size below 100 μm. The foam is produced by dissolving apolymer and a crosslinking agent in a solvent, after which a phaseseparation takes place in a polymer-concentrated phase and apolymer-diluted phase, and where crosslinking occurs in the concentratedphase. The produced foam is said to have an absorbent capacity of atleast 2 and preferably at least 10 g/g and be suited as an absorptionmaterial in for example diapers.

In EP-B-0 598 833 there is disclosed a foam material intended as anabsorbent structure of the above stated kind. The foam material has aspecified pore volume, specific surface area and ability to resume itsvolume after compression. The foam is a so called “HIPE”-foam (highinternal phase emulsion), which means that the foam is produced bypolymerization of a water-in-oil emulsion. The solid phase in the foamcreates a capillary system, which receives, distributes and storesliquid. There is no indication about the liquid storage capacity of thefoam measured by CRC (centrifuge retention capacity), which is a measureof the capacity of the foam to firmly bind liquid, so called gel liquid,in its solid phase by swelling the cell walls.

OBJECT AND MOST IMPORTANT FEATURES OF THE INVENTION

The object of the invention is to provide a foam material suited to beused as an absorbent structure in an absorbent article of the abovementioned kind and which has multifunctional properties in such a way,that it at the same time fulfils the function of a liquid acquisitionlayer, a storage layer and a distribution layer, namely the capacity toquickly receive liquid, distribute it in the structure and store it.

This has according to the invention been provided by the fact that thefoam material has an absorption rate at wetting of at least 0.4 ml/s fora round sample having the diameter 50 mm, a liquid distribution capacityat an inclination of 30° of at least 15 g/g and a liquid storagecapacity of at least 9% measured through CRC (centrifuge retentioncapacity), at which the test liquid in all cases is synthetic urine.

According to a preferred embodiment its absorption rate at wetting is atleast 0.5 ml/s, its liquid distribution capacity at an inclination of30° is at least 16 g/g and its liquid storage capacity is at least 11%measured through CRC.

It is also possible that the foam material in its pore system containsfibers.

The invention also refers to absorbent structures in absorbent articlessuch as diapers, pant diapers, sanitary napkins, incontinence guards,bed protections and the like, said absorbent structure containing aliquid absorbent open-cell foam material as disclosed above. Accordingto an embodiment said foam material is comprised as the single componentin the absorbent structure. According to a further embodiment the foammaterial has a three-dimensional anatomic shape.

DESCRIPTION OF DRAWINGS

The invention will in the following be closer described with referenceto the embodiments shown in the accompanying drawings.

FIG. 1 shows a measuring apparatus for measuring the absorption rate.

FIG. 2 shows an example of an absorption graph measured with themeasuring apparatus according to FIG. 1.

FIG. 3 shows a measuring apparatus for determining the liquiddistribution rate.

FIG. 4 a and b shows the pore volume distribution for a foam materialaccording to the invention.

FIGS. 5 and 6 show electron microscope pictures (ESEM) of a foammaterial according to the invention in dry and wet conditionrespectively.

FIGS. 7 and 8 show electron microscope pictures (ESEM) on a commerciallyavailable viscose foam (Vileda) in dry and wet condition respectively.

DESCRIPTION OF EMBODIMENTS

The invention refers to liquid absorbent foam materials with specificwell-defined properties which make them suited to use as absorbents forbody liquids, such as urine, blood and wound discharges. The foammaterial may thus be used as the entire or part of the absorbentstructure in absorbent articles such as diapers, pant diapers, sanitarynapkins, incontinence guards, wound dressings, bed protections etc.

A foam is built of a continuous three-dimensional network or cellularstructure of a solid or liquid phase, which surrounds a gaseous phasedispersed therein. In a polymeric foam the solid phase is a polymericmaterial, which forms the cell walls in the continuous cellular phase.The cells may have different shape, size and topography and be open orclosed. In this case the cell structure is open which means that thecells communicate with each other. The term foam as defined according tothe present invention also encompasses such materials where fibers ofdifferent types are integrated in the cell structure.

Polymeric foams are produced from the polymer itself or from themonomers which are to be polymerized possibly with the addition ofcrosslinking agents, foam forming additives and/or additives for cellstabilization. There are different methods for foam generation such asmechanical agitation, air injection, heating, gas generation,evaporation, enzymatic decomposition and phase separation techniques.

Several open-cell polymeric foam material function well as liquidabsorbents and can be heavily compressed, and then swell in contact withliquid, at which the liquid is absorbed into the cell structure of thefoam.

According to the invention such open-cell polymeric foam materials areconcerned which have multifunctional absorption properties with respectto liquid acquisition capacity, distribution capacity and storagecapacity. The material should thus be able to simultaneously fulfil thefunctions of a liquid acquisition layer, distribution layer and storagelayer.

According to a preferred embodiment of the invention the foam materialaccording to the invention constitutes the sole component of theabsorbent structure of the absorbent article. It can also replace theliquid pervious topsheet which normally covers the absorbent structureand which is intended to be located closest to the skin of the wearer.

In order that an absorption material will have the desiredmultifunctional properties it is required that it has a relatively broadpore volume distribution, i e it should in its capillary structurecontain pores with a varying mean pore size within the interval 0-500μm. The pore volume distribution (PVD) is determined by means of a PVDapparatus manufactured by Textile Research Institute, Princeton, USA.The function of the PVD apparatus is described in detail in Miller, B.and Tyomkin, L. Textile Reseach Journal 56 (1986) 35.

In order that a foam will have the multifunctional absorption propertiesaimed at it is desirable to have a distribution of its absorptioncapacity in the form of capillary liquid and gel liquid. Gel liquidrefers to liquid held in pores smaller than 3 μm and capillary liquidrefers to loosely bound liquid in pores larger than 3 μm and up to 500μm. Gel liquid is the liquid that is held most firmly in the structure.It is desirable that the gel liquid absorption, determined as the totalamount of liquid in pores below 3 μm according to PVD measurements, isat least 4 μg and preferably at least 5 μg of synthetic urine. Thecapillary liquid absorption determined as the total amount of liquid inpores between 3-100 μm according to PVD measurements, should be at least8 ml/g, preferably at least 10 ml/g.

As stated above the foam material according to the invention should havedefined values of liquid acquisition, distribution and storage capacityrespectively. Thus it should have an absorption rate at wetting of atleast 0.4 ml/s for a round sample having the diameter 50 mm, saidabsorption rate being determined by the below defined measuring methodfor liquid acquisition capacity. Preferably its absorption rate shouldbe at least 0.5 ml/s. The liquid distribution capacity at an inclinationof 30° should be at least 15 g/g and preferably at least 16 g/g,measured according to the below defined measuring method fordistribution capacity. The foam should further have a storage capacityof at least 9% and preferably at least 11% measured through the belowdefined measuring method for storage capacity (CRC=centifuge retentioncapacity).

Test Liquid

In all cases the test liquid was synthetic urine according to thefollowing recipe: 0.66 g/l MgSO₄, 4.47 μl KCl, 7.60 μl NaCl, 18.00 μlNH₂CONH₂ (urea), 3.54 g/l KH₂PO₄, 0.754 g/l Na₂HPO₄, 1 ml/l of a 0.1%solution of Triton X-100, which is a surfactant sold by Aldrich. Thesubstances were dissolved in deionized water.

Absorption Rate

The liquid acquisition capacity was measured according to the belowdescribed measuring apparatus for determining the absorption rate of asample. The measuring apparatus is shown in FIG. 1 and comprises a stand10 with a holder 11 for a glass filter plate (porosity 1, supplierWerner-Glas AB, Stockholm) and holder 3 for a thickness gauge 14. Theglass filter plate 12 is provided with a liquid (synthetic urine) from aglass bowl 15 placed on a scale 16. The holder II for the glass filterplate 12 is vertically adjustable which makes the hydrostatic pressureadjustable. The liquid level in the bowl 15 should be only 2 cm belowthe level of the glass filter plate 12. With this hydrostatic pressurepores up to 250 μm will be filled with liquid if the contact anglebetween the sample, which is placed on the glass filter plate 12, andthe liquid is supposed to be 70° The measuring signals from the scaleand the thickness gauge are transmitted to a computer with 15 datum/s atmeasuring periods of up to 60 seconds. At longer measuring periods thesignal speed becomes lower. The measurement is started automatically bymeans of a contact when the sample reaches the glass filter plate 12.The measurement result is printed by a printer as a function of time.

Round samples with the diameter 50 mm were punched out from the foammaterial. The foam material was conditioned before testing at least for4 hours at 50% relative humidity and a temperature of 23° C. The glassfilter plate 12 should be saturated with test liquid (synthetic urine)when the measurement is started. The samples are attached against theglass filter plate by a pair of minimal pieces of double-sided adhesivetape. The samples were loaded during the measurement with a pressure of0.57 kPa.

The absorption progress can be divided into three phases:

-   1) “The initial phase”. The sample absorbs liquid unevenly on the    surface that is in contact with the glass filter plate. First when    the entire surface is covered with liquid the next phase “steady    state” begins.-   2) “Steady state”. Here liquid spreads like a front up through the    sample, i e absorption takes place only in the z-direction. The    absorbed liquid amount increases linearly with time.-   3) “The finishing phase”. Here the liquid has reached the top of the    sample and begins to spread over the entire upper limiting surface.    When the entire upper surface is covered with liquid the absorption    stops.

One example of an absorption graph is shown in FIG. 2, at which thegraph I shows the absorption progress and graph II shows the change ofthickness of the sample during the absorption.

The absorption rate in “steady state” is calculated from the linear partof the absorption graph, where the absorbed liquid amount increaseslinearly with time, i e as the coefficient of direction and is expressedin ml/s.

Liquid Distribution Capacity

In this method the amount of liquid is measured which is absorbed anddistributed during 60 minutes by the material, which is placed with aninclination of 30°. Samples with the dimension 1.5×28 cm were punchedout. The samples were conditioned in 50% relative humidity (RH) and 23°C. for 24 h±2 h. The samples can then be stored dark in plastic bags forup to 14 days. The testings were performed in climate room 50% RH and23° C.

A measuring apparatus which is schematically shown in FIG. 3 were usedat the testings. The measuring apparatus comprises a scale 17, a plexiglass plate 18 and a liquid container 19, in which the liquid surface isindicated with 20. The liquid container 19 is placed adjacent the scale17, at which it is important that both take a horizontal position. Theplexi glass plate 18 is placed on the scale with an inclination of 30′with respect to the horizontal plane without touching the liquidcontainer 19. Test liquid is poured into the liquid container 19, sothat 20 mm of plexi glass plate is below the liquid surface 20. Thesample is weighed with an accuracy of measurement of 0.1 g and is placedon the plexi glass plate 18 without the sample touching the liquid. Thescale is then calibrated. The sample is then moved along the plexi glassplate 18 so that 20 mm of the sample will be below the liquid surface, ie the end of the sample will be 10 mm below the liquid surface as seenin the vertical direction, after which the sample is fixed in thisposition with a clamp. After exactly 60 minutes the measurement isinterrupted and the sample is weighed again. It is also measured howlong distance of the sample has been wetted on the underside and on theupperside respectively. The liquid distribution capacity is calculatedas: m₂/m₁ (gig) where

m₂ is the weight of the sample after the measurement, andm₁ is the dry weight of the sample before the measurement.

Storage Capacity

The storage capacity of the foam was measured according to the so calledCRC method (centrifuge retention capacity). This involves that thesample is allowed to absorb liquid freely until saturated and isweighed, after which weight_((saturated)) is obtained. Then the sampleis centrifugated during 1o minutes at 1500 rpm, which approximatelycorresponds to a load of 300 g. The sample is weighed aftercentrifugation, at which weight_((centrifugated)) is obtained. By thencalculating the quotient between weight_((centrifugated)) andweight_((saturated)) and multiply with 100 the storage capacity of thesample in percent is obtained.

Method for Producing a Foam Material According to the Invention

Below there is disclosed a method for producing a foam materialaccording to the invention. As a first step of the foam production apolymer solution is prepared by dissolving a polymer in a solvent,preferably water. The polymer is preferably a polymer containingfunctional crosslinkable groups, e g carboxy-, hydroxy- or amino groups,e g a polysaccharide or polypeptide. Examples of useful polysaccharidesare carboxy methyl cellulose (CMC), carboxy ethyl cellulose, starchderivatives etc.

In the case of CMC a suitable concentration of the polymer solution is0.5-10% by weight, at which water is used as solvent. This concentrationmust however be adapted to the polymer used.

Then there is added a suitable surfactant and by mechanical agitation afoam is created. Alternatively air injection is used for creating thefoam. Possibly one or more different surfactants are added to thesolution to control the properties of the foam such as porosity andstability.

In case it is desired that the foam should contain fibers these arepreferably added in connection with the foaming of the polymer solution.The fibers are mainly used for improving the mechanical properties ofthe produced foam. On one hand the ability of the foam to withstand bothtensile and shearing forces will increase and on the other hand it willbe more compressible, i e it can be compressed to high densities and yetexpand at wetting. The latter of course improves the capillaryabsorption capacity of the foam after compression and since oftenthinness of absorbent articles are strived for fiber addition can givespecial advantages. Besides fiber addition can improve the liquiddistribution properties of the foam.

Suitable fibers are different types of hydrophilic natural or syntheticfibers. Preferably pulp fibers are used, especially chemical pulp.

When using CMC as the polymeric substance an alkaline compound ispreferably added, e g NaOH, for activating the CMC to react with thecrosslinking agent. The amount of the alkali relative to the amount ofcrosslinking agent effects the reaction speed, which increases at anincrease of the alkali amount. The order of addition betweenpolysaccharide (CMC), surfactant, possible fibers and alkali may bevaried and it is also possible to mix all components at the same time.It is however important that they are well mixed and that air orpossibly some other gas can be mixed into the material so that a porousfoam is formed. The method of mixing and foam formation can bemechanical agitation, gas injection or extrusion under press reduction.

In the next step the crosslinking agent should be added. It is heredesired to have a homogeneous distribution thereof in the materialbefore the crosslinking reaction starts. It can therefore beadvantageous to work at low temperatures, since the temperature isimportant for the reaction speed. The foam may for example be cooled toa temperature close to 0° C. before the crosslinking agent is added. Itcan however be possible to achieve good results also with room temperedfoams especially if the alkali addition is reduced.

Suitable crosslinking agents are cyanuric chloride, formaldehyde,dimethyl urea, diepoxides, glutaraldehyde, glyoxal, divinyl sulphone,epichlorhydrine etc. The crosslinking agent is added under strongmechanical stirring in order to obtain a good mixing. The crosslinkingagent can possibly be dissolved in a small amount of solvent in order toenhance the distribution of the crosslinking agent in the foam.

After this step the viscous but liquid foam is shaped by placing it in asuitable mould. After then the foam is frozen. After thawing of thefrozen foam this has transferred from a liquid condition to a solid,porous and liquid absorbent condition with unique properties withrespect to liquid acquisition, distribution and storage capacity.

According to a theory to which however the invention is not bound thefollowing things happen during the freezing step:

a) Water concentrates in the form of ice crystals, which break up thefoam structure and makes it porous after removal of the water. Thiseffects the absorption capacity of the material in a favourable way.b) As a result of the separation of water in connection with theformation of ice crystals there will be a concentration of polymerbetween the ice crystals. This makes the polymer chains coming closer toeach other, at which the reduced distance between the polymer chainsincreases the opportunities to crosslinking reactions.c) The water separation also makes that the alkali content close to thepolymer chains increases, which make them more disposed to react withthe crosslinking agent.

After freezing and thawing the foam is washed in order to removeundesired chemicals and secure so that the material is innoxious fromproduct safety point of views. This step is preferably combined withdeswelling of the material and removal of water. The foam is herewithwashed with a suitable solvent which can deswell the foam and dissolvethe water. Examples of such solvents are ethanol, acetone and methanol.Finally the material is dried by evaporating the liquid.

The foam thus prepared has a solid porous structure and is also soft andflexible. It has excellent absorption properties which makes it suitableto use in different types of absorbent articles mentioned above. It mayalso be shaped into a desired three-dimensional shape, which isdetermined by the shape of the mould in which the foam is applied duringthe freezing step. The foam can be compressed to a high density, andthen swell again while absorbing liquid. The latter property is veryinteresting if the foam is to be used in thin products.

Examples 1-3 below describes production of some different types of foammaterials according to the invention and table 1 describes theabsorption properties of the materials in comparison to some referencematerials.

Raw Materials Used at the Foam Production

Cekol 50000 Carboxy methyl cellulose from Metsä Chemicals Highly viscousquality with a substitution degree of about 0.8. Celpol RX Carboxymethyl cellulose from Metsä Chemicals. Highly viscous quality with asubstitution degree of about 1.2. Softwood sulphate SCA Graphic Paper,Sundsvall, Sweden. pulp Cyanuric chloride Merck-Schuchardt. Degree ofpurity: For synthesis. Berol 048 Nonionic surfactant from Akzo Berocell451 Anionic surfactant from Akzo Nobel. Sodium hydroxide EKA Nobel.Degree of purity: min 97%. Methyl ketone E. Merck. Degree of purity: Forsynthesis.

Example 1

A liquid foam was produced by vigorous mixing with an electric beater ofthe following mixture: 220 g of a 3% solution of Celpol RX in water,2.82.g bleached softwood sulphate pulp, 80 g water, 0.13 g NaOH, 1.0 gBerocell 451 and 1.0 g Berol 048. The foam was cooled to a temperatureof about 2° C. after which 0.264 g of cyanuric chloride dissolved in 5 gmethyl ethyl ketone was added to the foam mixture.

After vigorous stirring for 3 minutes the foam was spread to a layerwith an area of about 1600 cm² on a plane plastic surface (PVC) and wasfrozen at about −18° C. After about 20 hours the frozen foam wasreleased from the plastic surface and was thawed in a water bath. Awater swollen but insoluble foam was obtained. It was washed anddeswollen by leaching in ethanol and was dried at room temperature.After drying the solid foam was compressed by pressing it between rollsin a laboratory calendar of the mark Külsters to a bulk of about 3.0cm³/g.

Example 2

Two liquid foams were prepared by vigorous mixing of the two followingmixtures:

1. 110 g of a 3% solution of Celpol RX in water, 1.41 g bleachedsoftwood sulphate pulp, 40 g water, 0.057 g NaOH, 0.5 g Berocell 451 and0.5 g Berol 048.2. 110 g of a 3% solution of Cekol 50000 in water, 1.41 g bleachedsoftwood sulphate pulp, 40 g water, 0.091 g NaOH, 0.5 g Berocell 451 and0.5 g Berol 048.

Both foams were cooled to a temperature of about 2° C. after which 0.264g cyanuric chloride dissolved in 5 g methyl ethyl ketone was added tothe first mentioned foam mixture. After vigorous stirring during about 3minutes the foams were mixed carefully for about 2 minutes.

After that the foam was spread out to a layer with an area of about 1600cm² on a plane plastic surface (PVC) and was frozen at about −18° C.After about 20 hours the frozen foam was released from the plasticsurface and was thawed in a water bath. A water swollen but insolublefoam was obtained. This was washed and deswollen by leaching in ethanoland was dried at room temperature. After drying the solid foam wascompressed by pressing it between rolls to a bulk of about 3.1 cm³/g.

Example 3

Two liquid foams were manufactured by vigorous mixing of the followingmixtures:

1. 110 g of a 3% solution of Celpol RX in water, 1.41 g bleachedsoftwood sulphate pulp, 40 g water, 0.057 g NaOH, 0.5 g Berocell 451 and0.5 g Berol 048.2. 110 g of a 3% solution of Cekol 50000 in water, 1.41 g bleachedsoftwood sulphate pulp, 40 g water, 0.091 g NaOH, 0.5 g Berocell 451 and0.5 g Berol 048.

Both foams were cooled to a temperature of about 2° C. after which 0.264g cyanuric chloride dissolved in 10 g methyl ethyl ketone was added tothe first mentioned foam mixture. After vigorous mixing for about 3minutes the foams were mixed carefully during about 2 minutes.

After that the foam was spread out to a layer with an area of about 1600cm² on a plane plastic surface (PVC) and was frozen at about −18° C.After about 20 hours the frozen foam was released from the plasticsurface and was thawed in a water bath. A water swollen but insolublefoam was obtained. This was washed and deswollen by leaching in ethanoland was dried at room temperature. After drying the solid foam wascompressed by pressing it between rolls to a bulk of about 2.4 cm³/g.

Measurement Results of Absorption Properties

In Table 1 below the measurement results are shown concerning absorptionrate, liquid distribution capacity and liquid storage capacity, whichwere measured for the different test foams 1, 2 and 3 according toExamples 1, 2 and 3 above as compared to some reference materials in theform of a pair of commercially available foam materials, viz. Viledafrom Freudenberg Household Products AB and Vibrofoam from Nova-Sorb Ltd.

TABLE 1 Distribution Material Abs. Rate (ml/s) capacity (g/g) Storagecapacity (%) Test foam 1 0.48 16.1 30 Test foam 2 0.53 18.8 26 Test foam3 0.63 24.2 12 Vileda 2.1  4.5 5.5 Vibrofoam 0.015 — 53

From these results it is seen that the foam materials according to theinvention have high absorption rate, liquid distribution capacity aswell as storage capacity, while the reference materials either had highabsorption rate (Vileda) or a high storage capacity (Vibrofoam).

Pore Volume Distribution Measurements (PVD)

The pore volume distribution of the foam materials according to example3 was determined by means of a PVD apparatus from Textile ResearchInstitute, Princeton. USA. The material was swollen in synthetic urineduring about 1 hour and its pore volume distribution was thendetermined. The material was tested with a mechanical load of 0.57 kPa.In FIG. 4 a there is shown the pore volume distribution and in FIG. 4 bthere is shown the cumulative volume, in e liquid in ml/g dry sample, inpores between 3 μm and the value noted on the x-axis.

In pore volume measurements liquid held in pores below 3 μm can not beremoved and the distribution graph thus only describes the pore volumedistribution in pores with the size 3 μm and larger. It is thereforepossible by weighing the sample after finished measurement to determinethe total liquid amount in pores below 3 μm. This liquid concentrationin gig dry material is defined as gel liquid and was at this measurement5.62 g/g.

Electron Microscope Pictures (ESEM)

The electron microscope pictures according to FIGS. 5 and 6 show a foammaterial produced according to example 3 in dry and wet conditionsrespectively, and from which it can be seen that the cell walls of thefoam material have swollen in connection with the absorption of liquid,which indicates that the solid phase of the foam takes an active part inthe absorption process. The electron microscope pictures according toFIGS. 7 and 8 show a commercially available viscose foam (Vileda) in dryand wet condition respectively, and in which it can be noticed only avery slight swelling of the cell walls in wet condition.

1. A liquid absorbent material comprising an open-cell polymeric foammaterial comprising either polysaccharide or polypeptide, the foammaterial comprising a distribution of pore sizes between 0 and 3 μm, thefoam material having an absorption rate at wetting of at least 0.4 ml/sfor a round sample having a 50 mm diameter, a liquid distributioncapacity at an inclination of 30° of at least 15 g/g, a liquid storagecapacity of at least 9% measured through centrifuge retention capacity,and an absorption of at least 4 g/g measured by pore volume distributionof total liquid amount in pores below 3 μm, for synthetic urine testliquid.
 2. The liquid absorbent material as claimed in claim 1, whereinthe absorption rate at wetting is at least 0.5 ml/s, the liquiddistribution capacity at an inclination of 30° is at least 16 g/g, andthe liquid storage capacity measured through centrifuge retentioncapacity is at least 11%.
 3. The liquid absorbent material as claimed inclaim 1, wherein the foam material contains fibers in its pore system.4. The liquid absorbent material as set forth in claim 1, wherein theliquid absorbent material is utilized as an absorbent structure in anabsorbent article and the absorbent article is a diaper, a pant diaper,a sanitary napkin, an incontinence guard, a wound dressing, or a bedprotection.
 5. The liquid absorbent material as set forth in claim 1,wherein the open-cell polymeric foam material is formed by a processwherein a removable phase is removed after a crosslinking step.
 6. Theliquid absorbent material as set forth in claim 5, wherein the removablephase is water.
 7. An absorbent structure in an absorbent article,wherein the absorbent structure comprises a liquid absorbent materialaccording to claim
 1. 8. The absorbent structure as claimed in claim 7,wherein said absorbent structure consists of said foam material.
 9. Theabsorbent structure as claimed in claim 7, wherein the foam material hasa three-dimensional anatomic shape.
 10. The absorbent structure in anabsorbent article as claimed in claim 7, wherein the absorbent articleis a diaper, a pant diaper, a sanitary napkin, an incontinence guard, awound dressing, or a bed protection.
 11. A liquid absorbent materialcomprising an open-cell polymeric foam material comprising eitherpolysaccharide or polypeptide, the foam material having a firstdistribution of pore sizes between 0 and 3 μm and a second distributionof pore sizes between 3 and 100 μm, the foam material having anabsorption rate at wetting of at least 0.4 ml/s for a round samplehaving a 50 mm diameter, a liquid distribution capacity at aninclination of 30° of at least 15 g/g, a liquid storage capacity of atleast 9% measured through centrifuge retention capacity and anabsorption of at least 4 g/g measured by pore volume distribution oftotal liquid amount in pores below 3 μm, for synthetic urine testliquid.
 12. A liquid absorbent material comprising an open-cellpolymeric foam material comprising either polysaccharide or polypeptide,the foam material having a first distribution of pore sizes between 0and 3 μm and a second distribution of pore sizes between 3 and 500 μm,the foam material having an absorption rate at wetting of at least 0.4ml/s for a round sample having a 50 mm diameter, a liquid distributioncapacity at an inclination of 30° of at least 15 g/g, a liquid storagecapacity of at least 9% measured through centrifuge retention capacityand an absorption of at least 4 g/g measured by pore volume distributionof total liquid amount in pores below 3 μm, for synthetic urine testliquid.
 13. A liquid absorbent material comprising an open-cellpolymeric foam material comprising either polysaccharide or polypeptide,the foam material having an absorption rate at wetting of at least 0.4ml/s for a round sample having a 50 mm diameter, a liquid distributioncapacity at an inclination of 30° of at least 15 g/g, a liquid storagecapacity of at least 9% measured through centrifuge retention capacity,for synthetic urine test liquid, a first distribution of pores with adiameter less than 3 μm which produces an absorption of at least 4 g/gsynthetic urine measured by pore volume distribution of total liquidamount in pores below 3 μm, and a second distribution of pores with adiameter between 3 and 100 μm which produces a capillary liquidabsorption of at least 8 ml/g.
 14. The liquid absorbent material asclaimed in claim 13, wherein the absorption in pores below 3 μm is atleast 5 g/g synthetic urine.
 15. The liquid absorbent material asclaimed in claim 13, wherein the capillary liquid absorption is at least10 ml/g synthetic urine.
 16. The liquid absorbent material as claimed inclaim 13, wherein the absorption in pores below 3 μm is at least 5 g/gsynthetic urine and the capillary liquid absorption is at least 10 ml/gsynthetic urine.